In a mobile network, it is known to use a heterogeneous deployment with high power base stations, also referred to as macro base stations, and low power base stations, also referred to as pico base stations. In such heterogeneous deployment, a conventional cell association mechanism, which is based on a downlink (DL) received signal strength as measured by a user equipment (UE), typically results in a limited coverage area of the pico base stations. The coverage area may however be extended by adding a bias or offset to the DL received signal strength of a pico base station as measured by the UEs, and using the biased DL received signal strength in the cell association mechanism. This mechanism is also referred to as cell individual offset (CIO). Using the CIO mechanism has the effect that also UEs near the cell border, which measure a lower DL received signal strength, will be associated with the cell so that the cell coverage area is extended. However, this may also have the effect that certain UEs experience a negative (on the logarithmic scale) Signal-to-Interference/Noise Ratio (SINR). In particular, the added bias may have the effect that a UE is associated with the pico base station, but the DL received signal strength from a macro base station is larger than the measured (unbiased) DL received signal strength of the pico base station. The interference from the macro base station is thus larger than the useful radio signal from the pico base station. The interference may affect both a data channel of the pico base station's cell and a control channel (CCH) of the cell. Specifically the interference on the CCH may prevent proper serving of the UE in the extended coverage area of the cell.
Accordingly, the offset which is added to the measured DL received signal strength needs to be suitably dimensioned. A too small value of the offset may result in a too small coverage area of the pico cell and therefore limit the capacity gain offered by the pico cell. A too high value of the offset may in turn result in unsuccessful cell association attempts of a UE, which is undesirable as well.
Accordingly, there is a need for techniques which allow for efficiently controlling radio transmissions in a mobile network in which the cell association of a UE can be controlled by configuring an offset to be added to a channel quality value, e.g., DL received signal strength, as measured by the UE.